Being famous may look enticing - the money, the adulation and the glamour all appear to be there for the taking. But why would anyone want to be push themselves into the public eye?

"Famous people have usually experienced a negative event during childhood - often it's the loss of a parent, or rejection from a key figure in their life at a younger age," said Professor Cary Cooper.

Prof Cooper, based at the University of Manchester Institute of Science and Technology, has written books exploring what drives people into the spotlight.

He said a common factor among famous people is that many are "not as self-confident as you think".

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Celebrities have often been put down during childhood, and told they would not achieve something - such as success at school, according to his theory.

He suggested that "their 'driver' - or motivator - is therefore to achieve something they thought they couldn't manage".

Senior psychologist Glenn Wilson, who works at the Institute of Psychiatry in London, added that you have to be a bit exhibitionistic and manipulative to desire fame.

People pursue the spotlight because they "love to be loved" - although this is "part of the problem", added Prof Cooper.

"When they're famous, celebrities begin to wonder if people love them for who they are, or for who they've become," he said.

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Concluding that it ends up "reinforcing their self-doubts", the professor said few famous people manage to have close relationships.

Painting a bleak picture, he added that their fame often takes them away from "ordinary people", and they're "thrown into a celebrity group of other people who are insecure".

"Why else would actors want to play other people - and why would they need the adulation of an audience?" he said.

And media coverage of celebrities' lives does not help matters, he added.

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"Stories about stars that get into the press are negative not positive - look at the sort of stories that hit headlines."

Dr Raj Persaud, a consultant psychiatrist at the Bethlem Royal and Maudsley Hospitals in south London, has also explored the nature of celebrity.

He reported that Canadian psychologist Mark Schaller argued that exposure to fame inevitably produces psychological disturbance.

The famous become more chronically self-conscious and self-aware because of all the attention, according to Mr Schaller's research.

When they're famous, celebrities begin to wonder if people love them for who they are, or for who they've become

Prof Cary Cooper

His findings suggest there is significantly more self-obsession in the writings of celebrities after they become famous, compared with before.

Famous people constantly experience that "merely momentary discomfort" of heightened self-consciousness you feel when someone points a camera at you, said Dr Persaud.

And Prof Cooper said celebrities often suffer from depression, and turning to drink or drugs could be a result of them often feeling "lonely when not on stage".

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Being away from home a lot, being under the scrutiny of the press, difficulty sustaining relationships - all of this "makes them vulnerable" and often has a "stress-related outcome".

Dr Persaud added that the highs and lows of fame's uncertainty "leave one drained, doing more and more bizarre things in order to court attention" - which eventually leads to losing credibility with your audience.

But despite this, it is not all doom and gloom, as for as Prof Cooper is concerned.

"The good news is they have a bounceback factor - they expect to be rejected and not to win.

"Celebrities who achieve longevity are people who make it on the basis of bouncing back - their 'driver' is very important," he said.

And, of course, the public's fascination with celebrities helps fuel their fame. But why do people find them so exciting?

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Prof Cooper said it is all about our need for "communality" - a feeling of belonging.

"We talk about people in the public eye and use people as metaphors in public life for our own lives.

"We use them as a common view - as a vehicle to test things out in our own lives. We look at their behaviour and ask ourselves whether it is 'right' or not."

But he added that we do not actually care about them as individuals - unfortunately for the celebrities we are interested only in "how their own lives might reflect our own".